Gas turbine engines (“GTE”) have been engineered extensively to improve efficiency, thrust-to-weight ratios, and other measures of engine performance. One of the most direct manners by which engine performance can be improved is through increases in the core rotational speeds and turbine inlet temperatures generated during engine operation. However, as turbine inlet temperatures and rotational speeds increase, so too do the thermal and mechanical demands placed on the GTE components. The most demanding performance requirements are typically placed on the high pressure turbine rotor or rotors, which are positioned immediately downstream of the GTE combustion section and which rotate at the greatest speed during engine operation. The turbine blades, in particular, are directly exposed to combustive gas flow at or near peak temperatures and are consequently heated to exceedingly high temperatures at which most alloys weaken or melt and become prone to oxidation or other forms of chemical degradation. By comparison, the inner portion of the turbine (commonly referred to as the “turbine disk”) is largely shielded from direct exposure to combustive gas flow, but is subject to considerable mechanical stressors resulting from the centrifugal forces acting on the turbine rotor at high rotational speeds.
Considering the variance in operating conditions across the turbine rotor, it is desirable to produce the turbine blades from a first alloy having good mechanical strength and oxidation resistance at highly elevated temperatures, while the turbine disk is fabricated from a second alloy having exceptionally high mechanical strength properties (e.g., high stress rupture strength and fatigue resistance) at lower operational temperatures. In one manufacturing technique for producing a dual alloy turbine rotor, the turbine disk and individual turbine blades are separately fabricated as individual pieces; e.g., the turbine disk may be forged and machined, while each turbine blade may be separately cast and machined. The turbine blades are fabricated to include enlarged base portions or shanks, which are inserted into mating slots provided around the outer circumference of the turbine disk. The shanks and mating slots are formed to have an interlocking geometry (e.g., a so-called “fir tree” interface), which prevents disengagement of the shanks in a radial direction during high speed rotation of the rotor.
While enabling fabrication of the turbine blades and the rotor disk from disparate alloys, the above-described manufacturing technique is limited in several respects. The formation of the geometrically complex mating blade interface between the shanks and the turbine disk slots often requires multiple precision machining steps, which add undesired expense, time, and complexity to the manufacturing process. In addition, the mating interface between the shanks and the turbine disk can be difficult to seal and may permit undesired leakage across the turbine rotor during engine operation. As a still further limitation, the formation of such a mating interface between the shanks and the turbine disk may necessitate an increase in the overall size and weight of the multi-piece turbine rotor to achieve a structural integrity comparable to that of a single-piece or monolithic turbine rotor.
It is thus desirable to provide embodiments of a method for the manufacture of turbine rotor enabling the turbine blades to be joined to a separately-fabricated rotor disk in a manner that overcomes the above-noted limitations; e.g., in a manner that reduces the cost and complexity of manufacturing, that reduces leakage across the turbine rotor, and that allows a reduction in the overall size and weight of the turbine rotor. Ideally, embodiments of a such a manufacturing method could also be utilized in the production other types of turbine engine components, such as compressor rotors, static turbine nozzle assemblies, seal plates, and engine frame structures. Finally, it would be desirable to provide embodiments of specialized tooling suitable for usage in such manufacturing processes. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.